Computer Network - Basic Concepts (Computer Network, Internet, Network Protocol)

This is a way for hosts to directly connect to other hosts through communication links. But if the distance is long and the number is large, how to ensure interconnection?

Interconnecting hosts through a switched network

After the host is connected to the switching network, it is connected to other hosts; among them, a very important component of the switching network is the switching node, that is, the switch or router .

What is the Internet

angle of composition details

It is the world's largest Internet network, the " network of networks " interconnected by ISP (Internet Service Provider) networks.

ISP is the abbreviation of Internet Service Provider, that is, Internet service provider.

Just like a user has to go to a telecommunications company to install a phone, if a user wants to access the Internet, he has to go to an ISP. ISP is the entrance for users to access the Internet.

Usually, an individual user's computer or a group user's computer network is first connected to the ISP's host through a certain communication line, and then accesses the Internet through the ISP's connection channel.

The role of ISP mainly has two aspects:

1. Provide Internet access services to users;

2. Provide users with various information services, such as email services, information release agency services, etc. Users can choose the ISP that suits them based on the network bandwidth, network access methods, service items, charging standards and management measures provided by the ISP.

is a collection of millions of interconnected computing devices

Computing devices such as hosts are also called end systems. They are capable of running a variety of network applications, interconnected by communication links such as fiber optics, copper cables, radio, satellite, and more.

Through switching network interconnection, routers and switches perform data packet switching , that is, forward packets (data packets). Learn more about this later.

Service perspective

Communication infrastructure that provides communication services for network applications

Web, VoIP, email, online games, e-commerce, social networks, etc.

Provide application programming interface, or API , for network applications

Support applications to "connect" to the Internet and send/receive data;

Provides data transfer services similar to the postal system.

but,

With only hardware (hosts, links, routers...) connections, the Internet cannot run smoothly, and the orderly delivery of application data cannot be guaranteed, so protocols were introduced .

What is a network protocol

introduce

Protocols are an important guarantee for the orderly progress of computer networks.

One thing we need to know is that hardware (hosts, routers, communication links, etc.) is the foundation of computer networks.

Data exchange in computer networks must comply with pre-agreed rules .

Just like in the transportation system, with the foundations of roads, infrastructure and means of transportation, traffic rules also need to be constrained and managed, otherwise the transportation system will easily be paralyzed.

Any communication or information exchange process requires rules

In human conversations, such as asking for time, asking questions, recommending people, etc.; we all have to follow a time rule,

When we communicate, we need to send a specific message to the other party, and the other party must take specific "actions" after receiving the message.

When communicating on the Internet, you also need to abide by certain rules, except that the communication subject is a "machine" rather than a person, exchanging "electronic" or "digital" messages.

All communication processes in computer networks must comply with certain/certain rules, which is what we call protocols .

definition

Network protocol , referred to as protocol for short , is a rule, standard or convention established for data exchange in the network.

The protocol specifies the format, meaning, sequence of messages exchanged between communication entities , and the "actions" taken in response to received information or events that occur .

Three elements of the agreement

Syntax _

The structure or format of data and control information, signal levels.

Semantics _

What control information needs to be sent;

What actions are performed and what responses are made;

Error control.

Timing _

sequence of events;

Speed matching.

importance of agreement

The protocol regulates all information sending and receiving processes in the network

For example, TCP (Transmission Control Protocol),

IP (Internet Protocol),

HTTP (Hypertext Transfer Protocol ) ,

HTTPS (Hypertext Transfer Protocol Secure),

UDP ( User Datagram Protocol ),

TFTP ( Trivial File Transfer Protocol ),

TCP/IP protocol and so on.

It is one of the important contents of learning network and one of the manifestations of network innovation.
Internet protocol standards

On the Internet, any user can propose his own solutions or specifications for problems in a certain area of the Internet and submit them to the Internet Engineering Task Force ( IETF ) as Internet Drafts (ID) . The draft is stored on working document sites in the United States, Europe and the Asia-Pacific region for discussion, testing and review by voluntary IETF members from many countries around the world. Finally, the Internet Engineering Steering Group (IESG) determines whether the draft can become an Internet standard.

If an Internet draft is not recommended by the IESG for publication as a standard after 6 months of existence on the relevant IETF site, it will be removed from the above site. In fact, at any time, an Internet Draft may be replaced by a new draft version and restart its 6-month storage period.

If an Internet draft is determined by the IESG as an official working document of the Internet, it will be submitted to the Internet Architecture Board (IAB) and formed into a sequentially numbered RFC document, which will be promulgated to the world through the Internet by the Internet Society (ISOC).

Reprinted from: What does RFC mean? - Know almost

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Learn from: MOOC Computer Network - Li Quanlong , Nie Lanshun